Corn coarse fiber (also known as pericarp or bran) is the outer covering of a kernel of corn, and is a product that can be used as feedstock for the production of such end products as Corn Fiber Gum (CFG) and Corn Fiber Oil. Corn Fiber Gum can be used in both food and non-food applications as a film former, an emulsifier, a low-viscosity bulking agent, an adhesive, or as a substitute for gum Arabic. Corn Fiber Oil has three natural phytosterol compounds (ferulate phytosterol esters or "FPE," free phytosterols or "St," and phytosterol fatty acyl esters or "St:E") that have been found to lower serum cholesterol in blood, and therefore can be used as a nutraceutical product. Such products command high dollar values in the market (approximately $8.00 to 9.00 per pound).
Currently, there are the following three primary methods for recovering pericarp: (1) wet-milling; (2) dry-milling; and (3) alkali debranning. In the corn wet-milling process, corn kernels are steeped for a period of between twenty-four and thirty-six hours in a warm solution of water and sulfur dioxide. Such steeping softens the kernels for grinding, removes soluble materials (which are dissolved in the steep water), and loosens the protein matrix within which the starch is embedded. The mix of steeped corn and water is fed to a degerminating mill, which grinds the corn such that the kernels are torn open and the germ is released. As the germ is lighter than the remainder of the slurry, it floats to the top of the slurry. This fact that the germ is of a lighter density than the remainder of the slurry enables the germ to be separated out from the slurry through the use of a hydrocyclone. The remaining slurry (which now lacks the germ, but includes starch, protein and fiber) is finely ground using an attrition mill to liberate the remaining endosperm attached to the fiber and to totally disrupt the endosperm cellular structure. The finely ground slurry is then passed through a series of screens to separate the fiber out of the slurry, and to wash the fiber clean of starch and protein. The washed fiber is then de-watered using fiber presses, and is finally dried. In this process, fine fiber (or the cellular material inside of the corn kernel) is also recovered with the pericarp (or corn coarse fiber). One disadvantage of obtaining pericarp by using a wet-milling process is that such processes involve large capital expenditures in equipment.
In the dry-milling process, clean corn is adjusted to about a twenty percent moisture content, and is then processed in a degerminator. In the degerminator, the moist corn is treated with an abrading action that strips the bran (pericarp) and germ away from the endosperm while still leaving the endosperm intact. The degerminator is set up so that the large pieces of endosperm proceed through to the end of the degerminator, while the pericarp and germ pass through screens on the underside of the degerminator. The mix of pericarp and germ is dried, cooled, and aspirated to separate the pericarp and the germ from each other. One disadvantage of obtaining pericarp from the above-described dry-milling process is that the pericarp obtained contains only low amounts of Corn Fiber Oil therein. Also, the dry-milling process just described does not result in ethanol production, so there is no additional income from ethanol sales.
In the third method of recovering pericarp from corn, alkali debranning, the pericarp is recovered by the chemical action of an alkali such as calcium hydroxide, potassium hydroxide, or sodium hydroxide. The process involves soaking corn kernels for a short period of time (between one and sixty minutes) in a hydroxide solution at temperatures ranging from ambient to about 100.degree. C. The alkali reacts with the connecting tissue between the endosperm and the pericarp, and loosens the coating so that mechanical or hydraulic action on the corn kernels results in the removal of the pericarp from the intact whole corn kernel. In this process, pure pericarp is recovered with no fine fiber (cellular material). However, the disadvantages of this process are that there are special disposal procedures required for the alkali, and that there is also a relatively high ash content in the pericarp.
One of the many end-products in which corn is used as the base-product is ethanol. Currently, ethanol is being produced from corn mainly via two different processes--a wet mill process and a dry-grind process (which is not to be confused with the dry-milling process described above). In wet milling, corn is separated into its different components (germ, fiber, protein, and starch) using various separation techniques, such as described above. The clean starch is then cooked, saccharified, fermented, and distilled to make ethanol. Wet milling is a very capital intensive process, but these costs are offset by the resulting high value co-products of the process (such as corn oil produced from the germ, gluten meal from the protein, and gluten feed from the fiber and solubles).
In the other primary process for producing ethanol, the dry-grind process, raw corn is ground, mixed with water, cooked, saccharified, fermented, and then distilled to make ethanol. However, while the only fermentable product in corn is the starch, the other non-fermentable components of the corn (the germ, the fiber, and the protein) are carried through the remainder of the dry-grind processing steps, and are recovered at the end as distillers dried grains with solubles, or DDGS. In current dry-grind processes, neither the germ nor the pericarp are recovered separately, but instead these components end up as part of the DDGS.
The dry-grind process is not a very capital intensive process (when compared with the wet-mill process), but the primary co-product produced (distillers dried grains, or DDG, which is a livestock feed product) is a relatively low value product. Accordingly, because of the low value co-product, the net corn cost is higher in dry-grind ethanol plants that it is in wet-mill plants. Thus, when corn prices increase, it is very difficult to economically justify operating dry-grind ethanol plants that can only produce low value co-products with the ethanol. Thus, many dry-grind ethanol plants shut down or reduce their production volume when corn prices increase.
The present inventors have realized that one strategy for reducing the net corn cost in dry-grind ethanol plants is to recover co-products other than DDGS, especially non-fermentable co-products. Previously, the present inventors studied modifications to conventional dry-grind ethanol plants that enabled the recovery of the germ. This modified dry grind ethanol process is known as the "Quick Germ" process, and involves soaking whole kernel corn in water before degermination. The germ is then recovered by germ hydrocyclones, and the remainder of the corn is ground and processed for ethanol production. Economic analysis has shown that the "Quick germ" process has the potential to reduce the cost of ethanol production by between 0.33 to 2.69 cents/liter. Although such cost reductions (primarily realized through the sale of the germ) have been helpful, further cost reductions are still necessary for dry-grind ethanol plants to remain competitive.
One object of the present invention is to provide an improved method of recovering pericarp from corn.
An additional object is to provide a method of recovering pericarp using flotation.
Another object of the present invention is to provide a method for extracting a high value co-product (pericarp) from dry-grind ethanol production processes so that such processes can be made more economically viable, especially when corn prices increase.
Still another object of the present invention is to provide a method of recovering pericarp without the disadvantages described above.
Other objects of the present invention will be discussed or will become apparent from the following description.